The present invention is directed to bicycle transmissions and, more particularly, to features in an apparatus for assisting a speed change operation in the bicycle transmission.
Various devices have been developed to help reduce the effort needed to operate bicycle transmissions such as derailleurs and internal hub transmissions. Examples of such devices particularly suited to assist the operation of derailleur transmissions are shown in U.S. Pat. No. 5,358,451. The devices shown therein for assisting the operation of a rear derailleur employ multiple moving parts that are in constant motion, thus increasing the amount of moving mass as well as the possibility of premature wear on the components. Devices shown therein for assisting the operation of a front derailleur accommodate only two front sprockets. However, many bicycles have more than two front sprockets. Thus, there is a desire for an assist device that can be used with more than two sprockets.
Some assisting devices use electric motors or solenoids to control the assisting operation. The electric motor or solenoid may operate for the entire shifting operation or for only a part of the shifting operation, and it is often necessary to provide cams or other mechanical control structures to control the amount of involvement of the motor or solenoid. Such control structures often have an intricate structure or require complicated cooperation between the structures.
Furthermore, such motors or solenoids often are placed in a location where they will encounter large operating forces. This requires the motors and solenoids to have a heavy-duty construction, thus increasing the size, weight and cost of the device. However, even heavy-duty motors and solenoids may operate improperly, and it is desirable to know when such faulty operation occurs. Thus, there is a need for an assist mechanism wherein electronic components can be manufactured to function reliably at a reasonable cost.